Fig. 82.--_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M. pectoralis minor; _d_, long portion of caput mediale of M. triceps; _e_, M. coracobrachialis; _f_, Mm. teres major and latissimus dorsi; _g_, intermediate portion of caput mediale of M. triceps; _h_, deep layer of M. pectoralis major; _i_, superficial layer of M. pectoralis major; _j_, M. anconeus; _k_, short portion of caput mediale of M. triceps; _l_, M. pronator teres; _m_, M. flexor carpi radialis; _n_, second head of M. flexor profundus digitorum; _o_, third and fourth heads of M. flexor profundus digitorum; _p_, M. palmaris longus; _q_, M. flexor carpi ulnaris.
Fig. 83.--_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M. infraspinatus; _d_, M. teres minor; _e_, long portion of caput mediale of M. triceps; _f_, M. coracobrachialis; _g_, _g′_, M. brachialis; _h_, intermediate portion of caput mediale of M. triceps; _i_, M. anconeus; _j_, short portion of medial head of M. triceps; _k_, M. pronator teres; _l_, second and third heads of M. flexor profundus digitorum; _m_, M. palmaris longus; _n_, M. extensor carpi ulnaris.]
_Insertion_ (Fig. 86, _d_).--The lateral surface of the ulna from the distal margin of the semilunar notch to the proximal end of the olecranon. The muscle covers the capsule of the joint and is closely adherent to it.
_Relations._--Outer (dorsal) surface with the caput laterale (Fig. 75, _h_) and the intermediate portion (Fig. 80, _j_) of the caput mediale. Inner surface with the bones and the capsule of the joint.
_Action._--Keeps the capsule tense and probably rotates the ulna slightly so as to pronate the hand.
3. =Muscles of the Antibrachium or Forearm.=
_Fascia of the Forearm._--The muscles of the forearm are not in contact with the skin, but are covered by the strong =antibrachial fascia=. This consists of two layers. The =superficial= one is a continuation of the general subcutaneous fascia of the arm; it covers the forearm as a continuous sheet which becomes thinner distad, and is finally lost near the wrist. The =deep= layer forms a dense, tendinous sheet which is closely applied to the muscles. It begins partly as a continuation of the general fascia of the arm, partly from the tendons of the triceps and epitrochlearis muscles. The sheet is attached to the dorsal surface of the ulna, between the extensor carpi ulnaris and the first head of the flexor profundus digitorum. It surrounds the forearm as a continuous sheath. On the lateral surface it dips between the extensor muscles, becoming closely attached to them and forming a partial sheath for each; it is attached with special firmness to their tendons. On the medial side of the arm the fascia passes smoothly over the flexors without dipping between them; it is continuous, however, with the border of the pronator teres, and distad of this muscle it is firmly attached to the radius.